1. Field of the Invention
This invention relates to the winding of a traveling paper web, such as is produced by a papermaking machine. More particularly, this invention relates to the construction of either a support drum or a rider roll, or both, for use in a winder for winding such a traveling paper web. Still more particularly, this invention relates to the construction of a support drum or rider roll having an elastomeric cover having a unique combination of Poisson""s ratio, absolute hardness and effective hardness to provide a relatively soft nip in support of the wound paper roll while utilizing a relatively hard elastomeric cover.
2. Description of the Prior Art
In the papermaking industry, a common form of winder for winding the substantially endless paper web produced by the papermaking machine comprises a pair of spaced, parallel support drums for supporting the wound paper roll being wound from the traveling paper web.
It is known in the papermaking industry to have winder support drums with grooves to permit the paper roll being wound to be turned with the purpose of encouraging less slippage between it and the support drum. Also, such grooves may provide a means to reduce any boundary layer air film between the drum and the paper roll. Such grooves can take several forms, such as, for example, spiral grooves, Chevron, or herringbone patterned.
It has also been contemplated to cover the support drums with an elastomeric material, such as rubber, in an attempt to provide a larger support area for the increasingly heavy wound paper roll on the cylindrical surface of the support drum. Some of such rubber covered drums have also been grooved. Examples of prior art types of grooving and support drum covers are shown in U.S. Pat. Nos. 1,867,550; 3,098,619; 4,541,585 and British Patent No. 417,769. While the prior art includes roll and support drums having elastomeric covers, the practice heretofore in the papermaking industry was to construct these covers with a hardness of 85 Shore xe2x80x9cAxe2x80x9d, or greater; only rarely have covers had a hardness as soft as 75 Shore xe2x80x9cAxe2x80x9d. On the Shore xe2x80x9cAxe2x80x9d scale, readings approaching 100 are relatively hard, and readings approaching 25 are relatively soft.
Grooved winder drums, grooved elastomeric covered winder drums and elastomeric covered winder drums all have some operational advantages and efficiencies which are generally associated with their ability to better support the paper roll being wound with less slippage, less internal stress, and more control of the winding process and desired parameters. This is particularly true during periods when the rotational speed of the wound paper roll is changing. However, such prior configurations also had inherent deficiencies.
If the non-grooved elastomeric material was too hard, it essentially operated like a solid metallic support drum, which negated any advantage, such as a larger support area, that an elastomeric cover provides. Softer elastomeric covers, which might provide such a larger wound web roll support area, were not believed to be economically or operationally viable.
Therefore, while fundamental configurations, such as providing support drums with elastomeric covers and grooving such drums, have long been known, there has been a long-felt need for a paper winder support drum having a grooved elastomeric cover which provides a relatively softer, wider nip and relatively long service during operation.
The problems, deficiencies and inefficiencies associated with prior art types of winder support drums having elastomeric covers have been obviated by this invention. In the winder support drum of this invention, an elastomeric cover is provided which has a unique combination of physical parameters and properties which enable it to operate continuously while supporting a wound paper roll on its grooved elastomeric surface. These properties include a Poisson""s ratio for the elastomeric material of about 0.47-0.499; an absolute hardness of the elastomeric material of about 65 Shore xe2x80x9cAxe2x80x9d, or less, for support drums; an absolute hardness of about 75 Shore xe2x80x9cAxe2x80x9d, or less, for rider rolls; and a surface pattern in the elastomeric cover which is so arranged that the percent of volumetric void for a unit volume of the cover is such that the effective hardness of the cover is much less than the intrinsic hardness of the cover. The absolute hardness range for rider roll elastomeric covers is somewhat higher on the Shore xe2x80x9cAxe2x80x9d scale (i.e. harder) due to the higher nip cycle frequency of the rider rolls which is a function of the differences in roll diameters between support drums and rider rolls (support drums have larger diameters).
The groove pattern in the cover surface need not have any particular configuration. While a dimpled surface pattern on the elastomeric cover is functionally superior, a diamond-shaped pattern or a tight spiral groove pattern is preferred. A symmetrical diamond pattern minimizes roll steering and thrusting forces. A tight spiral groove pattern minimizes noise and is more economical to make.
A cover having a plurality of individual circular impressions, each extending ring-like about the circumference of the roll, is not preferred due to the likelihood that the superpositioning of a similarly depressed layers will result in a very unattractive ridge pattern on the surface of the wound web roll.
These characteristics of the winder support drum construction enable the instant center associated with the nip between the wound paper roll and the support drum to be shifted from inside the wound paper roll to inside the elastomeric cover of the support drum. This combination of physical parameters and characteristics of the support drum also result in an effectively much softer cover, which is desirable from a standpoint of lowering the unit pressure on the support drum surface, while providing the durability and longevity of a much harder cover.
It is contemplated that the absolute and effective hardnesses of rolls used as support drums in a two-drum type of winder do not both have to be the same. Thus, it is contemplated that the effective hardness of the back drum cover, commonly referred to as the number one drum in the papermaking industry, might be harder than the effective hardness of the cover on the front drum (number two drum).
The principles of this invention can also be applied to the rider roll in a winder for winding a wound paper web roll. Therefore, in this description, the covers described can refer to either a support drum or a rider roll which are intended to be referred to by the generic term xe2x80x9crollxe2x80x9d in this description.
Accordingly, it is an object of this invention to provide an improved support drum or rider roll for a winder for winding a traveling paper web into a wound roll.
Another object of this invention is to provide an improved winder support drum or rider roll having an elastomeric cover.
Still another object of this invention is to provide an improved winder support drum or rider roll having an elastomeric cover with an open pattern in its surface.
Yet another object of this invention is to provide paper web winding apparatus for reducing interlayer shear stress between layers of the web in the wound web roll.
An advantage of this invention is a winder support drum or rider roll having an elastomeric cover which has an absolute hardness which is relatively high, and an effective hardness which is relatively low.
A feature of this invention is an elastomeric covered winder drum where the elastomer has a Poisson""s ratio of about 0.47 to about 0.499 and an effective hardness of about 55 Shore xe2x80x9cAxe2x80x9d, or less.
A feature of this invention is an elastomeric covered rider roll where the elastomer has a Poisson""s ratio of about 0.47 to about 0.499 and an effective hardness of about 65 Shore xe2x80x9cAxe2x80x9d, or less.
These, and other objects, features and advantages of this invention will be readily apparent to those skilled in the art when the description of the preferred embodiments is read in conjunction with the attached drawings.